Novel asymmetrical twin-core photonic crystal fiber for gain-flattened Raman amplifier

A novel asymmetrical twin-core photonic crystal fiber was proposed, whose effective overlap core area A _eff can be designed to synchronize the variation of Raman gain coefficient with respect to frequency. This fiber possesses a higher and flatter Raman gain efficiency coefficient curve r _R=g _R/A _eff over a specified band of wavelength than a conventional fiber. Therefore, it is a good candidate of gain medium for a flat, broad gain band fiber Raman amplifier. It was numerically demonstrated that for the Raman gain efficiency r _R, relative fluctuations of less than 2.2% and 5.7% are achievable in the C (1530−1565 nm) band and L (1565−1625 nm) band, respectively. Supported by the National Natural Science Foundation of China (Grant Nos. 60588502, 60607005, 60877033), the Science and Technology Bureau of Sichuan Province (Grant No. 2006z02-010-3) and the Youth Science and Technology Foundation of UESTC (Grant No. JX0628)